1. On the relative risk of medical incapacity or impairment while driving Eric Schmedding

2. Brussels, 25 nov 2005Second MEDRIL workshop Content Two types of risk and one criterium Two types of risk and one criterium Relative Risk in the assessment of incapacity: epilepsy Relative Risk in the assessment of incapacity: epilepsy The equation of risk for incapacity The equation of risk for incapacity Relationship between RR and COSY Relationship between RR and COSY Difference for the assessment of impairment: vision Difference for the assessment of impairment: vision Relative Risk: why use it ? Relative Risk: why use it ? What if…? – no theory What if…? – no theory

3. Brussels, 25 nov 2005Second MEDRIL workshop Second Working Group on Epilepsy and Driving of the European Union: members Mr Joël Valmain Mr Joël Valmain Dr Jaume Burcet Darde Dr Jaume Burcet Darde Dr Bernhard Gappmaier Dr Bernhard Gappmaier Prof Guenter Kraemer Prof Guenter Kraemer Dr John Kirker Dr John Kirker Dr Mikael Ojala Dr Mikael Ojala Dr Nicole Markschies Dr Nicole Markschies Dr Eric Schmedding Dr Eric Schmedding Dr Anders Sundqvist Dr Anders Sundqvist Dr Elena Valdès Dr Elena Valdès Prof Hervé Vespigniani, Prof Hervé Vespigniani, Dr Graham Wetherall Dr Graham Wetherall Dr Jörgen Worm-Petersen Dr Jörgen Worm-Petersen Traffic Bureau EU Traffic Bureau EU Spain Spain Austria Austria Germany Germany Ireland Ireland Finland Finland Germany Germany Belgium Belgium Sweden Sweden Spain Spain France France United Kingdom United Kingdom Denmark Denmark

4. Brussels, 25 nov 2005Second MEDRIL workshop Criteria for two types of risks ? For the population: For the population: “A” attributable risk A = The % of the population at risk because of the disease * ( R – 1 ) A = The % of the population at risk because of the disease * ( R – 1 ) A = P ( R – 1 ) A = P ( R – 1 ) For the driver: For the driver: “R” relative risk R = a ratio of risks: The risk of people with the disease / the risk of people without the disease The risk for the population remains low as long as "R" is reasonable

5. Brussels, 25 nov 2005Second MEDRIL workshop A = Attributable risk A = Attributable risk A = P ( R – 1 )P = 0.6*70% A = P ( R – 1 )P = 0.6*70% A = 0.42 ( 2.0 – 1 ) = 0.42 % A = 0.42 ( 2.0 – 1 ) = 0.42 % RR-1 RR-1 1 1 P (no epilepsy) P (no epilepsy) Total population with a licence Total population with a licence “A”: Risk for the population

6. Brussels, 25 nov 2005Second MEDRIL workshop How much is 0.42% ? European Union 2001 accidents per million European Union 2001 accidents per million Injury- accidents 3400 Injury- accidents 3400 Serious (+ fatal) accidents 710 Serious (+ fatal) accidents 710 So 0.42% would be:3 serious So 0.42% would be:3 serious including0.4 fatal

7. Brussels, 25 nov 2005Second MEDRIL workshop “R”: who runs the risk? > 60% of the risk is for the driver Europe: 61% of all fatalities are drivers Europe: 61% of all fatalities are drivers USA:68% USA:68% the remaining risk shared by the passengers > = other road users the remaining risk shared by the passengers > = other road users driverspassengers others driverspassengers others 60% ca 25%ca15% 60% ca 25%ca15% If passengers are present, the risk for them rises up to the driver´s level !

8. Brussels, 25 nov 2005Second MEDRIL workshop The quest for a criterium -population level There are few data (but none from Europe) about the risk for the individual driver with epilepsy but theoretically the risk is low for the population There are few data (but none from Europe) about the risk for the individual driver with epilepsy but theoretically the risk is low for the population

9. Brussels, 25 nov 2005Second MEDRIL workshop Two types of risks For the population: For the population: “A” attributable risk A = The % of the population at risk because of the disease * ( R – 1 ) A = The % of the population at risk because of the disease * ( R – 1 ) A = P ( R – 1 ) A = P ( R – 1 ) For the driver: For the driver: “R” relative risk R = a ratio of risks: The risk of people with the disease / the risk of people without the disease The risk for the population remains low as long as "R" is reasonable A "R" of 2-3 is very acceptable and should not lead to inability to drive

10. Brussels, 25 nov 2005Second MEDRIL workshop Acceptable for epilepsy ?

11. Brussels, 25 nov 2005Second MEDRIL workshop The quest for a criterium -driver level The criterium for driving should be based on the risk for the patient, rather than on the risk for the population The criterium for driving should be based on the risk for the patient, rather than on the risk for the population Relative risks up to 3 (6?) are accepted for some groups within the population Relative risks up to 3 (6?) are accepted for some groups within the population Relative risks of 2 – 4 could be acceptable for patients Relative risks of 2 – 4 could be acceptable for patients

12. The quest for a criterium The relation between the Relative Risk and the COSY RR 2 – 3 is COSY 20% - 40% COSY = Chance of an Occurrence of a Seizure in the next Year Incapacity: epilepsy

13. Brussels, 25 nov 2005Second MEDRIL workshop Factors in the equation of risk 1. exposure acute/chronic impairment 2. acute incapacity 3. accident 4. Outcome (fatalities) r = (R-1).F/(DX) DrXFDrXF

14. Brussels, 25 nov 2005Second MEDRIL workshop Factors in the equation of risk 1. D = 0.04 acute/chronic impairment 2. COSY = 20% (r = 0.2) 3. X = 0.6 4. F = 0.00014 r = (R-1).F/(DX) DrXFDrXF

15. Brussels, 25 nov 2005Second MEDRIL workshop Factors in the equation of risk r = (R-1).F/(DX) 4. F = 0.00014 1. D = 0.04 acute/chronic impairment 2. COSY = 20% (r = 0.2) 3. X = 0.6 D r X F From the COSY to the personal risk increase: R F/(DX) = 0.183 r = COSY (in %) /100 R = individual risk ratio (compared to someone who does not have epilepsy) F = fatal casualty rate per driver per year (1 / 7250 drivers) in the population D = proportion of time spent at the wheel (1 hour = 0.042) X = probability of a seizure at the wheel leading to a fatality (0.6*0.03 = 0.018) COSY = 2% R = 1.1 COSY = 10%R = 1.5 COSY = 20%R = 2.1 COSY = 30%R = 2.6 COSY = 40%R = 3.2

16. Recurrence risk The COSY decreases with the length of the seizure-free period

17. Brussels, 25 nov 2005Second MEDRIL workshop Model for the next occurrence of a randomly occurring event Criterium line

18. Brussels, 25 nov 2005Second MEDRIL workshop Recurrence before seizure-free period 3 mo 6 mo 12 mo 3 mo Relative Risk23

19. Brussels, 25 nov 2005Second MEDRIL workshop Recurrence after seizure-free period 3 mo 6 mo 12 mo 3 mo X mo 3 mo Europe Cosy 20% = RR 2.1 Relative Risk23

20. Brussels, 25 nov 2005Second MEDRIL workshop Different approach: the use of RR Impairment Impairment Identification of the relevant Identification of the relevant functions functions RR per function and per RR per function and per impairment category impairment category Cut-off value (e.g. RR > 2 ? ) Cut-off value (e.g. RR > 2 ? ) Test Test function while driving Confounding variables Importance of adaptive behaviour Measurement instruments Robust? Reproducible? Face value? "cheat resistance"? Incapacity Incapacity How likely is it to occur while driving? You need the co-operation of the patient Determine the COSY Compare with the criterium Calculation Calculation

21. Brussels, 25 nov 2005Second MEDRIL workshop Impairment: the use of RR Impairment Impairment Identification of the relevant functions Identification of the relevant functions RR per function and per impairment category RR per function and per impairment category Cut-off value (e.g. RR > 2 ? ) Cut-off value (e.g. RR > 2 ? ). range

22. Brussels, 25 nov 2005Second MEDRIL workshop

23. Brussels, 25 nov 2005Second MEDRIL workshop Epilepsy: what´s in a word? Chance of having an accident Chance of having an accident Not increased in the group that is allowed to drive (OR: 0.95 CI: 0.88-1.02) Not increased in the group that is allowed to drive (OR: 0.95 CI: 0.88-1.02) Taylor, Chadwick, Johnson: “Risk of accidents in drivers with epilepsy” J Neurol, Neurosurg, Psychiatry 1996; 60:621-27 Taylor, Chadwick, Johnson: “Risk of accidents in drivers with epilepsy” J Neurol, Neurosurg, Psychiatry 1996; 60:621-27 Hugely increased in a pre-surgical group (frequent seizures) of 367 patients: 40 % at some point had a seizure while driving Hugely increased in a pre-surgical group (frequent seizures) of 367 patients: 40 % at some point had a seizure while driving 70 % of them (27% of the whole group) had, at one point in time, one or more accidents while driving. Of these 32% had physical damage themselves; 20% caused physical damage in others 70 % of them (27% of the whole group) had, at one point in time, one or more accidents while driving. Of these 32% had physical damage themselves; 20% caused physical damage in others Berg A et al: “Driving in adults with refractory localisation-related epilepsy” Neurology 2000; 54: 625-630 Berg A et al: “Driving in adults with refractory localisation-related epilepsy” Neurology 2000; 54: 625-630

24. Brussels, 25 nov 2005Second MEDRIL workshop Relative risk useful? Find RR not for groups (diseases), but for factors that influence driving Find RR not for groups (diseases), but for factors that influence driving Incapacity, e.g. Epilepsy: Incapacity, e.g. Epilepsy: COSY COSY Impairment, e.g. Vision: functions Impairment, e.g. Vision: functions Visual acuity RR<2 Visual acuity RR<2 contrast sensitivity contrast sensitivity glare sensitivity (= condition- dependent) glare sensitivity (= condition- dependent) visual field (binocular test) (UFOV) visual field (binocular test) (UFOV) diplopia… diplopia… Research

25. Brussels, 25 nov 2005Second MEDRIL workshop The rules as proposed for epilepsy group 2 are based on a COSY of 2%The rules as proposed for epilepsy group 2 are based on a COSY of 2% Driving time: times 5 Toll of accidents:times 3 Assessment: what to do with… Multiple RR´s Multiple RR´s Comorbidity or the side-effect of medication Comorbidity or the side-effect of medication Limited licence Limited licence No consistent advice on how to use it No consistent advice on how to use it Group 2 Group 2 More severe, but how? More severe, but how? 15 times as severe

26. Brussels, 25 nov 2005Second MEDRIL workshop Conclusions To find a criterium of acceptable risk, we should consider the risk for the person (RR), not the risk for the population (A, attributable risk) To find a criterium of acceptable risk, we should consider the risk for the person (RR), not the risk for the population (A, attributable risk) An "RR" of 2-3 is acceptable An "RR" of 2-3 is acceptable RR does not give the increase in risk compared to the population ! RR does not give the increase in risk compared to the population ! RR when studied in medical conditions for non- homogeneous groups is not usable as such. The RR has to be studied for well-defined subgroups RR when studied in medical conditions for non- homogeneous groups is not usable as such. The RR has to be studied for well-defined subgroups RR is usefull RR is usefull As criterium in risk assessment For reasons of consistency In explanation and thus motivation of the patient

27. Brussels, 25 nov 2005Second MEDRIL workshop No theory… …means no adequate scientific data …means no adequate scientific data For the chance of a period of incapacity in the next year (COSY) For the chance of a period of incapacity in the next year (COSY) For the RR of a certain function and a specific impairment category For the RR of a certain function and a specific impairment category …means no criterium for "non-disease" ( = no necessity to test or assess) …means no criterium for "non-disease" ( = no necessity to test or assess) …but will the theory be proven to be an improvement on common sense ?

28. Second MEDRIL workshop Brussels, 25 november 2005 eric.schmedding@az.vub.ac.be